U.S. Pat. No. 5,453,875 discloses a monocular telescope having a positioning member. This positioning member is a rotatably journalled shaft which is mounted perpendicularly to the optical axis and is fixedly connected at both ends to respective rotating knobs. Furthermore, this positioning member is displaceable perpendicularly to the optical axis. Three detent positions can be adjusted by displacing the actuating member perpendicularly to the optical axis and a gear ratio stage is assigned to each detent position. The focusing optic is operatively connected to the positioning member via the particularly selected gear ratio stage. The speed of the adjusting movement of the focusing optic is dependent upon the selected gear ratio stage.
A brochure of the Leica Company of 1998 having the number 910596 discloses a monocular telescope which includes a coarse drive and a fine drive for focusing to distances of between 3.95 meters and infinity for adjusting the focusing. The actuating element of the coarse drive is directly connected to the output shaft. The actuating element of the fine drive is operatively connected to the output shaft via a drag gear. The rotational movement of the output shaft is transmitted to a spindle via a toothed belt. A focusing optic is displaceable along the optical axis and is displaced along the optical axis by rotating the spindle.
This mechanical arrangement is disadvantageous because the drag gear assembly often does not operate precisely and the transmission ratio of the drag gear assembly changes over the course of years.